1. Field of the Invention
The present invention relates generally to methods and systems for determining the mass flow rate of a fluid, and more particularly to the operation of mass flow controllers (MFCs) and mass flow meters (MFMs).
2. Discussion of the Related Art
Many industrial processes require precise control of various process fluids. For example, in the semiconductor industries, mass flow meters (MFMs) are used to precisely measure the amount of a process fluid that is introduced to a process chamber. In addition to measuring the mass flow, mass flow controllers (MFCs) are used to precisely measure and control the amount of a process fluid that is introduced to a process chamber. It is to be understood that the term fluid as used herein applies to any type of gas or vapor to which controlled flow may be of interest.
Mass flow controllers and mass flow meters have well defined performance criteria that are guaranteed by the MFC suppliers. Customer processes are based on repeatable performances from the devices after initial installation and process tune up. Mass flow controllers and mass flow meters that drift (e.g. due to aging) or get clogged (e.g. due to contamination) will cause a loss of repeatability that causes the process characteristics to change and will lead to lower yield or even total loss of the product being manufactured. For example, as a mass flow controller ages, one cause of drift in the mass flow controller is due to an increase in valve leak.
To combat one or more of the above problems, the disclosed embodiments include a system and method for providing a self-validating mass flow controller that is configured to determine valve leak and sensor offset simultaneously. In addition, the disclosed embodiments may utilize the self-validating procedure for real time in-situ correction of a mass flow controller or mass flow meter's output for zero offset or zero drift in the presence of valve leak. This will enable the MFC or MFM to provide real time accurate information without requiring down time to make the measurements.